1. Field of the Invention
The present invention relates to semiconductor memory devices and more particularly to a semiconductor memory device including a plurality of memory blocks.
2. Description of the Background Art
In semiconductor memory devices, a defective memory cell is replaced by a spare memory cell to equivalently repair the defective memory cell and to improve the yield of products. The flexible redundancy method has been proposed as one of redundant circuit structures in which a spare memory cell for replacing and repairing such a defective memory cell is provided.
One example of conventional semiconductor memory devices having the flexible redundancy structure will be described briefly with reference to FIG. 49. The conventional semiconductor memory device shown in FIG. 49 includes sense amplifier blocks MX1, MX2, MX3, . . . MXn. The sense amplifier blocks shown in FIG. 49 are formed of a plurality of memory cells corresponding to one sense amplifier column. Sense amplifier block MX1 includes a spare row SR1 (may include a plurality of spare rows). By using spare row SR1 in sense amplifier block MX1, it is possible to replace and repair a memory cell in another block (sense amplifier block MX3, for example).
In the conventional semiconductor memory devices, operation of row circuitry is carried out after determination as to whether replacing and repairing using a spare memory cell is to be performed. Accordingly, access time is delayed because of the time necessary to determine spare replacement.
In order to prevent this problem, a memory block including a normal memory cell and a memory block including a spare memory cell are simultaneously selected and activated and, thereafter, data is finally written to or read from either of the memory blocks. However, this method increases power consumption, contrarily to the demand for reducing power consumption.